Plant sterols are substances found in a wide variety of plants such as edible plants including soybeans and rapeseeds and lumbers and they are also called phytosterols. Formal or technical names of these substances are, for instance, β-sitosterol, campesterol, brassicasterol and stigmasterol.
Plant stanols are also called phytostanols and formal or technical names of these substances are, for instance, β-sitostanol, campestanol, brassicastanol and stigmastanol.
In this specification, these phytosterols and phytostanols are generically referred to as “plant sterols” for convenience.
On the other hand, ester derivatives of plant sterols and plant stanols primarily have different formal or technical names depending on substances as counterparts for forming corresponding esters (such as fatty acids) and they are in general referred to as plant sterol esters (phytosterol esters) or plant stanol esters (phytostanol esters). Accordingly, in this specification, these phytosterol esters and phytostanol esters are generically referred to as “plant sterol esters” for convenience.
Sterol corresponds to Sterin in German language and plant sterol esters are also referred to as stearyl esters which are also included in plant sterol esters herein defined.
Plant sterol and cholesterol resemble in their structures and therefore, it has been known that it undergoes competitive inhibition when cholesterol dissolves into bile acid micelles to thus control the absorption of cholesterol in the intestines. As a result, plant sterol permits the reduction of the levels of the overall or total serum cholesterol and of the serum LDL-cholesterol. Accordingly, it has been known that plant sterol is effective for the prevention of diseases such as hyperlipemia, coronary disorders and heart diseases, the US Food and Drug Administration (FDA) has approved that any health-emphasis indication may be attached to a plant sterol ester (or phytosterol)-reinforced food, while the Japanese Ministry of Health and Welfare/Labor has likewise approved some foods to which a plant sterol (or a phytosterol ester) is incorporated, as Foods for Specified Health Use.
It has been reported that plant sterol is rather excellent in bioavailability (ability of a substance to be biologically utilized) as compared with plant sterol ester (Patent Document 1). Regarding bioavailability, however, it has also been reported that both of plant sterol and plant sterol ester show effects of reducing the serum-cholesterol level and effects of inhibiting the absorption of β-carotene, which are comparable level with each other (Non-Patent Document 1). Consequently, there is not any disadvantage in the application of plant sterol ester.
However, plant sterol, which is quite useful as has been discussed above, has such physical properties that it does not dissolve in water and that it may dissolve even in oil in a concentration of only about 1%. Accordingly, plant sterol has been considered to be a material whose application to foods is quite difficult. Under such circumstances, a plant sterol ester has been developed, which shows an excellent solubility in an oil phase, but the kinds of foods, into which the plant sterol ester can be incorporated, are limited to specific ones such as margarine, edible oils, and mayonnaise. This would be quite inconvenient because of such a contradiction that the ingestion of such a plant sterol leads to the simultaneous intake of a large quantity of edible oil. For this reason, it would be an urgent necessity to develop a plant sterol which can easily be dispersed or dissolved even in water. To solve such a problem, there have been done various investigations.
However, most of conventional techniques thus developed relate to methods which comprise the step of emulsifying the plant sterol with the use of a lipophilic emulsifying agent (such as sucrose esters of fatty acids, mono(poly)glycerin esters of fatty acids, polysorbate and lecithin) (Patent Documents 1 to 4) and the resulting preparations are inferior in the taste and texture. In addition, when the emulsion is converted into powder, the resulting powdery preparation is not always considered to be sufficient in its dispersibility in water and the stability in the resulting aqueous solution or dispersion.
Moreover, there have also been proposed various methods which make use of hydrophilic octenyl succinate-modified starch which has good taste (Patent Documents 5 to 7). The resulting products have considerably improved taste, but the powdery preparation derived from the resulting emulsion through conversion thereof into powder still suffers from a problem in dispersibility observed when dissolving the powder in water.
Furthermore, there has been developed a method which comprises the step of emulsifying plant sterol with the use of a sucrose ester of a fatty acid or a polyglycerin fatty acid ester while melting the sterol at a quite high temperature corresponding to its melting point ranging from 120 to 160° C. (Patent Document 1). In the practical preparation thereof, however, the use of a device for controlling the temperature higher than 100° C. would be accompanied by a variety of difficulties from the viewpoint of facilities and energy cost. In addition, the powdered preparation produced according to this method may be applied to any practical food product only with considerable difficulties since the powdered preparation shows very poor dispersibility in water and the re-solubilization thereof in water in turn requires the use of a high pressure homogenizer.
Plant sterol ester is in the form of a paste. Accordingly, when converting the emulsified liquid thereof into powder using dextrin (a basic material for powdering), the hygroscopicity of the resulting preparation is largely dependent upon the magnitude of the hygroscopicity of the dextrin used. Maltodextrin having a DE value ranging from 10 to 25 has a rather weak sweetness and a low hygroscopicity and therefore, it is widely and favorably used as a basic material for powdering, but dextrin having a high DE value (“powdered corn syrup” having a DE value of not less than 25) is naturally superior to the former in view of the dispersibility in water. In this connection, however, the dextrin having a high DE value (powdered corn syrup) conversely has a strong sweetness and a high hygroscopicity and therefore, when applying the same to a food, it may impart undesirable sweetness thereto and the storage stability of the food is adversely affected because of the hygroscopicity thereof. This would become a serious drawback when it is intended to apply the resulting plant sterol to wide variety of foods.
It has been reported that saccharides having a DE value ranging from 10 to 25 are suitably used from the viewpoint of hygroscopicity and water dispersibility thereof when powdering an emulsion of fats and oils (see Patent Documents 10 and 11), but dextrin whose DE value exceeds 10 has a strong sweetness and a high hygroscopicity as has been discussed above and accordingly, it is not necessarily considered as a good basic material for powdering. For instance, PINEDEX #3 having a DE value of 25 (available from Matsutani Chemical Industry Co., Ltd.) shows a good flowability as a powdery substance and is excellent in dispersibility in water, but the product may impart undesirable sweetness to a food containing the same incorporated therein.
It has been reported that a branched dextrin is favorable to improve the dispersibility in water of a spray-dried product derived from an emulsion of a plant sterol (see Patent Document 3), but the branched dextrin is in general dextrin containing branched moieties obtained by removing glucose and low molecular weight oligosaccharides from a product prepared by acting a liquefying amylase on starch and accordingly, the branched dextrin is completely free of any form of linkage other than α1→4 and α1→6 glucoside bonds, which are essential to the starch. Similarly, a highly branched cyclic dextrin is one whose ring structure is formed through hydrolysis and rearrangement of amylopectin clusters by acting a branch-forming enzyme on the linear chain amylose portions connecting amylopectin clusters (see Patent Documents 12 and 13) and accordingly, the cyclic dextrin is also completely free of any form of linkage other than α1→4 and α1→6 glucoside bonds, which are essential for naturally occurring starch. For this reason, these branched dextrins are digestible (hydrolyzable) with a digestive enzyme of the human origin. In addition, no reference has been made with respect to bioavailability of the product obtained through the use of these branched dextrins when powdering the plant sterol.
On the other hand, as dextrins having branched structures different from those observed for the foregoing branched ones, there have been known indigestible dextrins (see Patent Documents 8 and 9). This indigestible dextrin is composed of indigestible water-soluble dietary fibers and therefore, it has been incorporated into wide variety of foods and drinks. Furthermore, it has also been known that the indigestible dextrin can be used as a binder in the preparation of a granulated product (see Patent Document 15), but it has never been used in powdering plant sterol.
Patent Document 6 states that dietary fibers may be added to a plant sterol-containing composition inasmuch as the addition thereof does not adversely affect the intended effect of the composition and polydextrose is specifically described as an example of the water-soluble dietary fiber material. However, polydextrose is a chemically synthesized product and is considered to be a food additive in the United States. In addition, it has been pointed out that polydextrose is liable to cause diarrhea upon ingestion thereof in excess. Further, the Patent Document does not refer to any effect, for instance, dispersibility and bioavailability, observed when it is added to the plant sterol-containing composition.
Moreover, some articles state that a food containing a combination of a plant sterol with dietary fibers (in particular, β-glucan) shows a synergistic effect of reducing cholesterol content (see Patent Document 14). When applying them to foods, however, an important problem has still remained unsolved. For instance, some physical and/or chemical properties such as dispersibility in water and viscosity should further be improved.
Patent Document 1: JP-T-2003-047359;
Patent Document 2: Japanese Patent No. 3,535,147;
Patent Document 3: JP-A-2005-269941;
Patent Document 4: JP-T-2005-521397;
Patent Document 5: Japanese Patent No. 2,662,930;
Patent Document 6: JP-A-2004-75541;
Patent Document 7: JP-T-2005-529109;
Patent Document 8: JP-A-02-145169;
Patent Document 9: JP-A-02-154664;
Patent Document 10: JP-A-11-196785;
Patent Document 11: JP-A-11-193229;
Patent Document 12: JP-A-2003-049189;
Patent Document 13: JP-A-2003-049190;
Patent Document 14: JP-T-2004-519254;
Patent Document 15: JP-A-2003-250479; and
Non-Patent Document 1: Am. J. Clin. Nutr., 2004, 80:171-177.